1. Field of the Invention
This invention relates to test fixtures used in testing circuit boards and the like and, particularly, a test fixture adapted to make electrical contact with test sites which are both on-grid and off-grid.
2. Background Discussion
Circuit boards are commonly used devices in a vast number of electronic instruments. These circuit boards carry metal pathways which constitute circuits. In making these boards, either one or both sides of an insulator sheet is clad with metal and then a resist material is coated on the surface to outline the desired conductive pathway or circuit. The exposed metal is then leached away with an acid solution and then the resist material is dissolved to form the circuit, which may include enlarged portions called pads. Commonly, holes are drilled through the pads and the interior of the hole is sometimes clad with metal. These pads and holes normally constitute points where various electronic devices are attached to the board.
To insure the quality of these circuit boards, electronic testing equipment has been developed to automatically test circuits between any two test sites by physically contacting each test site with a metal probe and then passing electricity through the probes so that the electricity flows along the circuit between the two selected test sites. This flow of electricity indicates that the circuit between the test sites is properly functioning.
One type of electronic testing equipment employs a probe head including an array of probes arranged in a grid configuration. Each probe is positioned at an intersection of coordinants of the grid, and is wired to an electronic analyzer. The grid is simply a number of spaced apart X and Y coordinants were the spacing between coordinants is known. Thus, the wired probes have known grid positions. The positions of test sites on the circuit board, however, may not have the same grid configuration as the wired probes.
For a circuit board of a particular design, the test sites will be arranged in a unique pattern. In order to make electrical contact between the test sites on the circuit board and the wired probes in the probe head, an interface fixture is used. Each circuit board having this same pattern can be tested using the same interface fixture. However, when another circuit board having test sites arranged in a different pattern is to be tested, a new interface fixture must be used. In other words, each circuit board design requires a custom made interface fixture. The cost of the interface fixture is amortized over the number of boards tested. Thus, when a great number of boards are to be tested, the cost of the interface fixture is relatively inexpensive. However, if only a few circuit boards are to be tested, the interface fixture is very expensive and may even be prohibitive.